Currently, as described here, the only way to get the archived test results in a Pipeline job is through the currentBuild.rawBuild object and pulling an AbstractTestResultAction out of it to read test results. This involved whitelisting several external methods.

This is a lot of work to try and say, generate a slack message saying "Build BUILD failed, X/Y tests failed". How hard would it be to define a property on the currentBuild Global Variable live this: currentBuild.testResult.failCount ?